This disclosure relates to methods for cumene oxidation, and in particular to methods and systems for manufacturing cumene hydroperoxide.
Free radical cumene oxidation reactions are well known. They can be conducted in the presence of a water phase, the so-called xe2x80x9cheterogeneous wet oxidationxe2x80x9d method, or in the absence of a water phase, the xe2x80x9cdry oxidationxe2x80x9d method. The heterogeneous wet oxidation method is generally preferred, as the presence of water provides improved safety and control of the exothermic reaction, and also requires less capital investment.
Commercially, wet cumene oxidation is conducted by a continuous process using a cascade of at least two gas-sparged reactors, typically three to six, with a variable temperature profile. The main oxidation reaction products are cumene hydroperoxide (CHP, the desired product, which is often used to produce phenol and acetone), along with dimethylbenzyl alcohol and acetophenone. In addition, trace amounts of acidic byproducts, such as formic acid, acetic acid, and phenol, are also produced. These acidic byproducts may inhibit the oxidation reaction, resulting in a decrease in both rate and yield, as well as negatively affecting CHP selectivity. To prevent this, U.S. Pat. Nos. 3,187,055; 3,523,977; 3,687,055; and 3,907,901 variously teach that alkali metal bases, such as sodium hydroxide (NaOH), and bicarbonate salts of alkali metals, such as sodium carbonate (Na2CO3), can be used as additives to remove the trace acid impurities. The use of a dibasic salt such as sodium carbonate is known to be additionally effective due to its ability to buffer the pH of the mixture and prevent large pH variations. Strongly basic NaOH is generally not preferred due to its tendency to form a water-soluble salt with the product CHP, resulting in loss of the CHP-salt into the oxidate aqueous purge streams, thereby decreasing yields.
The alkali additives are usually added to the reactors as aqueous solutions, whereupon two immiscible phases form. The strong bubbling action from an air stream provides contact and mixing of the two mutually insoluble phases into a partially emulsified mixture. Intimate mixing of the two immiscible phases is critical to obtaining efficient neutralization of the organic acids present in the cumene-CHP organic phase, and special static mixers, as disclosed in U.S. Pat. No. 3,933,921, and counter-current extractors, as disclosed in U.S. Pat. No. 5,120,902, have been employed in the art to aid in their contacting. However, even with these devices the neutralization process is only partially effective because the effectiveness and degree of organic acid neutralization is highly dependent on physical mass transfer limitations between the two contacting, immiscible phases. As a result, the pH of the oxidate reaction mixture may not be well controlled, which results in reduced oxidation reaction selectivity and an increased potential for equipment corrosion.
In U.S. Pat. Nos. 5,767,322 and 5,908,962, an alternative cumene wet oxidation process is described wherein Na2CO3 and ammonia (NH3) are simultaneously added to the reactors to form a mixed alkaline salt, NH4NaCO3. Free ammonia is not present since ammonia reacts immediately with the by-product NaHCO3. This mixed alkaline salt, although not truly soluble in the organic oxidate phase, appears to provide improved mass transfer between the two immiscible phases and more effectively neutralizes the undesirable organic acids than Na2CO3 alone. However, in order to be effective the process disclosed in U.S. Pat. No. 5,908,962 must split the cascade of oxidation reactors into two parallel trains, and must employ a special water stream flow that is counter-current to the cumene feed stream. In practice it has been found that the Na2CO3, which is a strong base, must be added in very precisely controlled amounts in order to prevent the pH from varying widely, i.e., over 3 to 4 pH units. In addition this process requires the purchase of two alkaline agents and the installation of a complex piping arrangement to manage the myriad of recycle streams. Thus this complicated cumene oxidation system design requires high investment in equipment, labor, and costs.
In addition, in all of the above-mentioned wet oxidation processes, small amounts of the inorganic alkali or alkaline earth metal salts remain entrained within the product CHP-cumene oxidate organic stream, and these salts pass forward into the downstream process steps where they deposit on and foul various pieces of equipment. This problem is particularly troublesome downstream where the distillation column heat exchangers and reboilers foul with regularity while concentrating CHP. This salt fouling reduces heat transfer ability, increases steam consumption, and makes the separations ineffective. Periodic cleaning of these fouled heat exchangers is required, which mandates plant shut down and thus lost production. Such production losses are quite costly in terms of time, labor, associated monetary expenditures, and need to be avoided if at all possible. Installation of coalescer units after cumene oxidation and prior to concentrating the CHP, to filter out and remove the entrained inorganic salts, is disclosed in U.S. Pat. No. 5,512,175. Although this method can be effective, the coalescer units are very large and their purchase and installation requires a high investment cost. The special carbon-fiber coalescer filter elements used inside these units must be replaced on an annual basis, which is also quite costly.
Accordingly there remains a need in the art for a cost effective method and system for manufacturing cumene hydroperoxide that overcomes the drawbacks and disadvantages of the above-identified methods.
The above-mentioned drawbacks and disadvantages are overcome or alleviated by a method and system for manufacturing cumene hydroperoxide, comprising reacting cumene and oxygen in the presence of ammonia or aqueous ammonia, and in the absence of an additive comprising an alkali or alkaline earth metal, to form cumene hydroperoxide.
The system comprises means for producing cumene hydroperoxide from cumene and oxygen in the presence of aqueous ammonia, and in the absence of an additive comprising an alkali or alkaline earth metal.
Another embodiment of a system for cumene oxidation, equally applicable for either the wet or dry mode of operation, comprises a cumene feed in fluid communication with a reactor having a cumene hydroperoxide oxidate outlet; an oxygen feed in fluid communication with the reactor; and an ammonia feed in fluid communication with the cumene feed and/or the reactor, wherein the cumene feed, the oxygen feed, the ammonia feed, and the reactor are free of an additive comprising an alkali or alkaline earth metal. A distillation apparatus may be serially connected with the cumene hydroperoxide oxidate outlet.